Bad beat (whine whine whine!)

Played in a live NL multi table rebuy last night. It was my first in ages so I was really looking forward to it. Things didn't start too well but hung in there and eventually it was down to 2 tables.
I got a really good run of cards JJ, AQ, AQ. I managed to knock somone out each time. There was only four of us at the table at this stage and between me and another lad we had half the chips of the whole tourney.
My very next hand was KK, brilliant. The blinds were at 500/1000. My stack was 24000. The other big stack and my self were really battling it out so this was a great chance to put his blind under pressure.
UTG folded. I raised 8000( overkill I know but I wanted to take him on on my own and scare off the small stacks). The small blind folded and he called(big stack) with no hesitation.
Figured him for an ace with a fairly big kicker. The flop came K76 rainbow. Wonder flop for me. I decided no slow playing(we were on the bubble). I pushed all in, not minding if he folded as the pot was relatively big anyway.
He called, had to revise my guess then. Maybe K6 or K7. Either way I was sorted. I could not believe what he turned over.....A10o. What?!!
Of course the turn was a 8 and the river was a 9. Burnt!
Can someone please try and explain what he was thinking and why he called!
I'm actually not as angry as I could be though. I think I was fairly unlucky.
Any suggestions as to any other way I should have played it but I think it was a solid enough play. Love to get inside his head though!

There's no telling why folks call when they are an obvious dog. I was playing in the Prima 5K last night and a guy called my big raise (half his stack) with an A-3 offsuit. Of course he went on to win the hand and I was out. Was it a smart play, probably not as I had A-J suited - but he won...

They only thing I could think of was he probably thought you only had top pair at the most and he figured he could catch the Ace to beat you. Plus, he had some outs for a straight. Luck just happened to be on his side.